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Tenophages: a novel macrophage-like tendon cell population expressing CX3CL1 and CX3CR1.

ABSTRACT: Tendon disorders frequently occur and recent evidence has clearly implicated the presence of immune cells and inflammatory events during early tendinopathy. However, the origin and properties of these cells remain poorly defined. Therefore, the aim of this study was to determine the presence of cells in healthy rodent and human tendon tissue fulfilling macrophage-like functions. Using various transgenic reporter mouse models, we demonstrate the presence of tendon-resident cells in the dense matrix of the tendon core expressing the fractalkine (Fkn) receptor CX3CR1 and its cognate ligand CX3CL1/Fkn. Pro-inflammatory stimulation of 3D tendon-like constructs in vitro resulted in a significant increase in the expression of IL-1?, IL-6, Mmp3, Mmp9, CX3CL1 and epiregulin, which has been reported to contribute to inflammation, wound healing and tissue repair. Furthermore, we demonstrate that inhibition of the Fkn receptor blocked tendon cell migration in vitro, and show the presence of CX3CL1/CX3CR1/EREG-expressing cells in healthy human tendons. Taken together, we demonstrate the presence of CX3CL1⁺/CX3CR1⁺ 'tenophages' within the healthy tendon proper, which potentially fulfill surveillance functions in tendons.This article has an associated First Person interview with the first author of the paper.

SUBMITTER: Lehner C

PROVIDER: S-EPMC6918766 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Microglial polarization is a dynamic response to acute brain hypoxia induced by stroke and traumatic brain injury (TBI). However, studies on the polarization of microglia in chronic cerebral circulation insufficiency (CCCI) are limited. Our objective was to investigate the effect of CCCI on microglial polarization after chronic brain hypoperfusion (CBH) and explore the underlying molecular mechanisms. METHODS:CBH model was established by bilateral common carotid artery occlusion (2-vessel occlusion, 2VO) in rats. Using the stereotaxic injection technique, lenti-pre-miR-195 and anti-miR-195 oligonucleotide fragments (lenti-pre-AMO-miR-195) were injeted into the CA1 region of the hippocampus to construct animal models with high or low expression of miR-195. Immunofluorescence staining and flow cytometry were conducted to examine the status of microglial polarization. In vitro, Transwell co-culture system was taken to investigate the role of miR-195 on neuronal-microglial communication through CX3CL1-CX3CR1 signaling. Quantitative real-time PCR was used to detect the level of miR-195 and inflammatory factors. The protein levels of CX3CL1 and CX3CR1 were evaluated by both western blot and immunofluorescence staining. RESULTS:CBH induced by 2VO initiated microglial/macrophage activation in the rat hippocampus from 1?week to 8?weeks, as evaluated by increased ratio of (CD68+ and CD206+)/Iba-1 immunofluorescence. And the microglial/macrophage polarization was shifted towards the M1 phenotype at 8 weeks following CBH. The expression of CX3CL1 and CX3CR1 was increased in the hippocampus of 2VO rats at 8 weeks. An in vitro study in a Transwell co-culture system demonstrated that transfection of either primary-cultured neonatal rat neurons (NRNs) or microglial BV2 cells with AMO-195-induced M1 polarization of BV2 cells and increased CX3CL1 and CX3CR1 expression and that these effects were reversed by miR-195 mimics. Furthermore, the upregulation of miR-195 induced by lenti-pre-miR-195 injection prevented microglial/macrophage polarization to M1 phenotype triggered by hippocampal injection of lenti-pre-AMO-miR-195 and 2VO surgery. CONCLUSIONS:Our findings conclude that downregulation of miR-195 in the hippocampus is involved in CBH-induced microglial/macrophage polarization towards M1 phenotype by governing communication between neurons and microglia through the regulation of CX3CL1 and CX3CR1 signaling. This indicates that miR-195 may provide a new strategy for clinical prevention and treatment of CBH.

Project description:Hydrogen sulfide, as a novel gaseous mediator, has been suggested to play a key role in atherogenesis. However, the precise mechanisms by which H(2)S affects atherosclerosis remain unclear. Therefore, the present study aimed to investigate the potential role of H(2)S in atherosclerosis and the underlying mechanism with respect to chemokines (CCL2, CCL5 and CX3CL1) and chemokine receptors (CCR2, CCR5, and CX3CR1) in macrophages. Mouse macrophage cell line RAW 264.7 or mouse peritoneal macrophages were pre-incubated with saline or NaHS (50 µM, 100 µM, 200 µM), an H(2)S donor, and then stimulated with interferon-? (IFN-?) or lipopolysaccharide (LPS). It was found that NaHS dose-dependently inhibited IFN-? or LPS-induced CX3CR1 and CX3CL1 expression, as well as CX3CR1-mediated chemotaxis in macrophages. Overexpression of cystathionine ?-lyase (CSE), an enzyme that catalyzes H(2)S biosynthesis resulted in a significant reduction in CX3CR1 and CX3CL1 expression as well as CX3CR1-mediated chemotaxis in stimulated macrophages. The inhibitory effect of H(2)S on CX3CR1 and CX3CL1 expression was mediated by modulation of proliferators-activated receptor-? (PPAR-?) and NF-?B pathway. Furthermore, male apoE(-/-) mice were fed a high-fat diet and then randomly given NaHS (1 mg/kg, i.p., daily) or DL-propargylglycine (PAG, 10 mg/kg, i.p., daily). NaHS significantly inhibited aortic CX3CR1 and CX3CL1 expression and impeded aortic plaque development. NaHS had a better anti-atherogenic benefit when it was applied at the early stage of atherosclerosis. However, inhibition of H(2)S formation by PAG increased aortic CX3CR1 and CX3CL1 expression and exacerbated the extent of atherosclerosis. In addition, H(2)S had minimal effect on the expression of CCL2, CCL5, CCR2 and CCR5 in vitro and in vivo. In conclusion, these data indicate that H(2)S hampers the progression of atherosclerosis in fat-fed apoE(-/-) mice and downregulates CX3CR1 and CX3CL1 expression on macrophages and in lesion plaques.

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Tenophages: a novel macrophage-like tendon cell population expressing CX3CL1 and CX3CR1.

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